CFD/FEA Applied

The 2012 Newport to Bermuda Race was about record breaking speed and problem-free sailing in challenging conditions. This year’s overall fleet winner in the Gibbs Hill Lighthouse Division under both ORR and IRC was the 72′ Shockwave owned and skippered by George Sakellaris and powered by Doyle Sails. Key to Shockwave’s success was selecting the ideal inventory for conditions and the ability to deploy and furl her Code 0, with complete confidence and full control in very challenging conditions. The sail had to roll tightly, so it could be left up for periods of time. Doyle developed a unique top down furling Code 0 to make this a reality.

Most significant was Doyle’s use of high resolutions RANS CFD to analyze Shockwave’s sailing characteristics versus her sail carrying ability. Doyle analyzed five different sail combinations to evaluate the driving force versus heeling moment to determine the optimum sails to carry aboard for the race. Specifically the analysis compared a conventional double head rig, a mast head Code 0, a fractional Code 0, an A3 and an oversized reacher (a large LP headsail with penalty.) Initial CFD analysis revealed that Shockwave would require more power than the standard jib top and genoa staysail, double head rig could provide. Further analysis illustrated there would be a very narrow window where an A3 could be successfully carried from a stability standpoint. The free luff of the A3 would also make it a difficult sail to drive through waves. Yet, knowing that with the right sail combination Shockwave had break-a-way speed potential it was ultimately determined that a mast head Code 0 delivered the most driving force over a wider range of conditions for a given heeling force than the other combinations. The tight luff of the Code 0 provided additional benefits as well. The sail could be depowered without fear of collapse, and it would be very stable for driving hard in offshore conditions.

Difference in shape between a penalty reacher and a Code 0

The next step was to apply the CFD derived sail forces to a FEA structural model of the sails to determine the lightest Code 0 that could be built for Shockwave. The CFD/FEA analysis suggested that a sail half the weight of the existing Code 0 provided by another sailmaker. The weight savings would also make the sail much easier to handle.

Not satisfied with the current state-of-the-art in Code 0 furling Doyle partnered with Future Fibres and KZ Marine to develop top down furling for a Code 0 with an internal torque cable in the luff. Previously, top down furling has been used for free flying, downwind sails with the torque cable external to the luff of the sail. Shockwave’s Code 0 was designed from the outset to use top down furling gear with the torque rope in the luff. This new adaptation of top down equipment created a system that worked flawlessly during the race. The top down approach rolls the head of the sail very tightly and the tight roll continues down to the tack, compared to conventional furling gear that furls the sail tightly at the tack and loose in the upper leech where the roach often never furls properly. The tightness of the furl Shockwave minimized windage when the sail was left furled during rapidly changing conditions and greatly improved handling the sail. The crew was always confident that the sail could be deployed without prematurely unfurling and the tight furl made dropping the sail to deck much easier.

Ultimately, Doyle’s diverse engineering capabilities combining CFD/FEA, sail design and design of the sail handling systems for the Code 0 were a significant contribution to Shockwave’s victory over her newer rivals.